When a spark plug is energized for ignition of an internal-combustion engine, radio noise is generated from the spark plug. There has been known a method for reducing such radio noise by adjusting the distance between the forward end of a center electrode of the spark plug and the forward end of a resistor element thereof (Japanese Patent Application Laid-Open (kokai) No. 2006-66086).
In recent years, an increasing number of components of an internal-combustion engine have been made of resin for weight reduction. The resin components of the internal combustion engine are low in radio noise suppression performance. Accordingly, the spark plug is required to further suppress such radio noise by itself.
The present invention addresses the above-mentioned problem.